Crystalline ZnSe thin films have been deposited on polished GaAs(100) substrates by pulsed laser ablation of a single target of polycrystalline ZnSe solid using KrF 248 nm excimer laser. Chemical etching and high temperature heating were used for pretreatment of substrates. Atomic force microscopy (AFM) shows that the average roughnesses of ZnSe thin films can reach 3～4 nm. X ray diffraction (XRD) shows that FWHM of ZnSe (400) peaks are 0.4°～0.5°. Analysis of quadruple mass spectroscopy for laser ablated plumes indicates that the plumes consist of Zn, Se and 2Se. It was deduced that ZnSe thin film was grown in two dimensional mode.